Then they came out with ink cartridges for fountain pens. When the cartridge was empty, I used the previous ink bottle to refill the cartridge by squeezing the cartridge, sticking it in the ink bottle, and letting go so it would suck up ink.

Let's face it, ink cartridge manufacturers like to give you "low ink" or "empty" warning messages even when you know that can't be possible. However, there is an interesting hack that may work on some brands that will trick your computer into squeezing every last ounce left in it.